For the 20 states in which marijuana is legal, either for medicinal or recreational purposes, there’s a new challenge for law enforcement: judging whether stoned users are too impaired to drive.

On any given Friday and Saturday night in California, 7% of drivers on the road test positive for marijuana, according to the state’s first comprehensive roadside survey of alcohol and drug use while driving, conducted by the Pacific Institute for Research and Evaluation for the state’s highway department. That percentage is similar to the proportion of drivers who recorded some alcohol (not necessarily exceeding the legal limit for driving under the influence) in their blood.

While the survey does not address whether the positive tests resulted in impaired driving — more than 1,300 drivers were randomly pulled over and asked if they would participate in the study without any legal consequences resulting from the alcohol and drug testing — the study may help law enforcement officials to better understand how legalizing marijuana will impact driving decisions. Eighteen states, including California, currently allow marijuana for medical use, and Colorado and Washington became the first states to legalize recreational use — potentially creating a larger pool of stoned drivers.

Drivers in the survey were told that the results would be anonymous and would have no legal consequences, regardless of their blood alcohol levels (measured by a breathalyzer) or the results of the drug testing (from a saliva sample) for 50 drugs, including illegal substances, over-the-counter medications and prescription drugs. Participants also earned $20 for taking part, and those who had an unsafe blood alcohol concentration (BAC) or who seemed to be impaired were not arrested but were provided with alternative transportation for their safety. The survey targeted nine regions in the state where police officers pulled over potential participants between 10pm and midnight, and 1am to 3am during a Friday and Saturday night.

Although 7% of drivers tested positive for alcohol, most were not driving while drunk or impaired: 4.6% had a BAC less than the .05 cutoff for driving while impaired and only 1% had a BAC of over .08, the threshold for drunk driving.

However, because people who suspect they might be driving under the influence are far less likely to agree to stop for a survey, the research likely under-represents the real rate of potentially performance-impairing drug use by drivers.

But the results provide a useful window into how changing marijuana laws will affect those who toke up and get behind the wheel. Research suggests that stoned users on the road are not as impaired as those who drink alcohol are, and there is some evidence that those who use marijuana, particularly for medical purposes, may be staying off the roads anyway. A national survey conducted in 2007 found that on average, about 7.7% of drivers may test positive for marijuana, and despite California’s booming medical marijuana industry, for example, fewer drivers tested positive for marijuana in 2012 than did in 2010, when a similar survey by the Pacific Institute found 8.5% of those pulled over had used before driving, compared to 7.4% in the current survey.

In addition, the results suggest that contrary to what some critics of legalizing marijuana have feared, pot users are not smoking marijuana and drinking at the same time, a potentially undesirable combination on the road, which is more dangerous than simple drunk driving. The 2010 survey found that 1.3% of people behind the wheel tested positive for both; the figure was 1% for 2012. Of those marijuana users who also drank, none was found to be legally drunk but 69% showed blood alcohol levels in the impaired range.

The question of whether the people who test positive for marijuana are actually affected by the drug at the time they are driving, however, remains difficult to answer. The study used a cutoff level of 2 nanograms per milliliter of saliva of THC, the main psychoactive ingredient in marijuana. Driving within three hours of smoking pot is associated with a near doubling of the risk of fatal crashes. However, THC can remain in blood and saliva for highly variable times after the last use of the drug. Although the marijuana “high” only lasts three to five hours, studies of heavy users in a locked hospital ward showed THC can be detected in the blood up to a week after they are abstinent, and the outer limit of detection time in saliva tests is not known. While marijuana does not promote uninhibited and potentially reckless behavior like alcohol does, THC does have mild hallocinogenic and sedative effects, and studies show it can impair cognition and memory, making driving potentially more hazardous.

To address the question of how much pot makes driving under the influence of marijuana dangerous, Washington state’s law limits legal use in drivers who are pulled over to under 5 nanograms, regardless of any evidence of impairment. Opponents of the legalization, including some of those who use marijuana for medical reasons, felt the limit would unfairly snare many innocent medical users.

Washington, however, is an exception. Because of the scientific controversy over the link between marijuana fluid levels and impairing effects, few states have set standards for stoned driving detection. Colorado has debated them but legislators cannot come to an agreement.

They may have to soon, since the survey shows that drivers are toking up and getting behind the wheel. Studies clarifying how marijuana can affect decisions on the road will be more critical as more states grapple with legalization of the drug.

“Drugged driving poses a serious threat to public safety,” said Obama’s “drug czar” Gil Kerlikowske, in a statement released with the survey. “We commend the California Office of Traffic Safety for shedding light on this growing problem and for educating Californians about the prevalence of this danger.” And hopefully encouraging policy makers to support more research on better understanding marijuana’s effects on decision-making while driving.

Marijuana users are much better driving a car than alcohol drinkers, and are less likely to be driving while using. Marijuana is a very healthy food if taken as an edible, not smoked. It is a gentle and safe way to handle pain. There is a great $2.99 e-book on medical marijuana: MARIJUANA - Guide to Buying, Growing, Harvesting, and Making Medical Marijuana Oil and Delicious Candies to Treat Pain and Ailments by Mary Bendis, Second Edition. This book has great recipes for easy marijuana oil, delicious Cannabis Chocolates, and tasty Dragon Teeth Mints.

I just saw the times has linked to the dud study claiming medpot laws reduce crashes - bad reporting, the study has been widely and for good reason slated in the scientific community. It is a disgrace to its authors and fit for toilet tissue only. Is Soros an advertiser?

Kevin Hunt has presented superseded studies giving an imbalanced picture. He is wrong, over 100 studies have built a picture and consensus amongst traffic safety experts *(this excludes drug policy experts who pretend they understand the disciplin) of sole cannabis use being responsible for many road deaths globally. Having worked in the area analysing policy for a decade odd I can only express irritation at the reckless harm denial of cannabis legalisers who senselessly seem to equate admitting harm with supporting prohibition. To do so is not their M.O. and yes a few silly studies that have no scientific rigor have been produced by the likes of Rees and co. One should look closely to the funders etc. It is often George Soros behind such ppl and pulling strings. Also in the Government arena, likely why USA is dithering while germany and france have mass drug tested drivers for nearly a decade. And Australia does tens of thousands of saliva tests a year. The excuses thrown up about not being able to settle on what level of pot is impairing are a smokescreen, the science is clear. 3ng is where crash risk rises and over 5ng people are impaired in as many essential driving skill areas as if they were drunk. Its time for the States to carry out their prime function - protecting the right to life of road users, instead of pandering to the pot smoker vote. As they cry poor me while filling other families coffins. Sick.

Comparing traffic deaths over time in states with and without medical marijuana law changes, the researchers found that fatal car wrecks dropped by 9% in states that legalized medical use — which was largely attributable to a decline in drunk driving.

The best evidence around cannabis and MVCs comes from modern “culpability studies” from Australia and France, which found that crashed drivers who used cannabis were more likely to have caused the crash than drug- and alcohol-free drivers. However, this risk was relatively small—comparable to that associated with alcohol levels between 0 and 0.05%.

There is no evidence that consumption of cannabis alone increases the risk of culpability for traffic crash fatalities or injuries for which hospitalization occurs, and may reduce those risks. REFERENCE: M. Bates and T. Blakely. 1999. “Role of cannabis in motor vehicle crashes.” Epidemiologic Reviews 21: 222-232. In contrast to the compensatory behavior exhibited by subjects under marijuana treatment, subjects who have received alcohol tend to drive in a more risky manner. Both substances impair performance; however, the more cautious behavior of subjects who have received marijuana decreases the impact of the drug on performance, whereas the opposite holds true for alcohol.” REFERENCE: A. Smiley. 1999. Marijuana: On-Road and Driving-Simulator Studies. There was a clear relationship between alcohol and culpability. … In contrast, there was no significant increase in culpability for cannabinoids alone. REFERENCE: Logan, M.C., Hunter, C.E., Lokan, R.J., White, J.M., & White, M.A. (2000). The THC-only drivers had a responsibility rate below that of the drugfree drivers. … While the difference was not statistically significant, there was no indication that cannabis by itself was a cause of fatal crashes.” REFERENCE: K. Terhune. 1992. The incidence and role of drugs in fatally injured drivers. Washington, DC: US Department of Transportation National Highway Traffic Safety Administration, Report No. DOT HS 808 065.

“At the present time, the evidence to suggest an involvement of cannabis in road crashes is scientifically unproven. REFERENCE: G. Chesher and M. Longo. 2002. “Cannabis leads to a more cautious style of driving, [but] it has a negative impact on decision time and trajectory. [However,] this in itself does not mean that drivers under the influence of cannabis represent a traffic safety risk. … Cannabis alone, particularly in low doses, has little effect on the skills involved in automobile driving.” REFERENCE: Canadian Senate Special Committee on Illegal Drugs. 2002. Both simulation and road trials generally find that driving behavior shortly after consumption of larger doses of cannabis results in (i) a more cautious driving style; (ii) increased variability in lane position (and headway); and (iii) longer decision times. Whereas these results indicate a 'change' from normal conditions, they do not necessarily reflect 'impairment' in terms of performance effectiveness since few studies report increased accident risk. REFERENCE: UK Department of Environment, Transport and the Regions (Road Safety Division). 2000.

Using marijuana is always better than being drunk out of your mind and driving. If they want to just feel a little better or be in less pain they should try Medical Marijuana edibles, much safer! You don't have to use that much cannabis to get relief. This book has great information on how to make marijuana oil and great small candies!Great e-book on medical marijuana: MARIJUANA - Guide to Buying, Growing, Harvesting, and Making Medical Marijuana Oil and Delicious Candies to Treat Pain and Ailments by Mary Bendis, Second Edition. This book has great recipes for easy marijuana oil, delicious Cannabis Chocolates, and tasty Dragon Teeth Mints! goo.gl/iYjPn goo.gl/Jfs61

I do know traffic statistics as provided by the US Government covering several years of states that do vs states that don't have medical marijuana laws, that 'every' single state with medical marijuana, their alcohol sales went down by at the minimum 11% while other states without stayed stagnant. Teen suicides went down in EVERY medical marijuana state. Traffic fatalities were down 6% at a minimum in EVERY medical marijuana state, and stagnant or the same in most non medical states.

The numbers of statistical fact would indicate this may be more than folly.

@ChasHolman@RachaelFord Just to clarify - I am for decriminalisation but not by deceitful means and coruption Soros style, bribing officials and media with benefits is not a hallmark of a free society - he is a fascist.

@ChasHolman@RachaelFord Well they tried to dignify the thing with the term study, it was a discussion paper about the coincidences or associations you speak of that were quite non events in some places due to small number issues in most States looked at (disguised by the authors) & other strong factors like more drink drive policing and anti alcohol campaigns - 'study' was carefully tailored to propagate myths, and one that was a joke amongst many experts in statistics - generally these were PHds I conferred about it with. It was written for grabbing headlines in liberal media and not a serious effort from what we can see, I know several experts wrote long harsh critiques that the media of course failed to notice. Here is one of the more brief ones the authors declined a request from the publishing journal to actually address which really shows their highest value is not science - actually am having trouble putting it to google docs. If you're interested reply and I'll try harder...